KR20150117641A - A vacuum pump having a disconnectable drive coupling - Google Patents

Abstract

The vacuum pump drive is detachable from the drive shaft during movement of the piston against the return spring under the action of the offset pressure. The piston includes a speed synchronous clutch engageable with the input shaft to rotate the piston at the speed of the input shaft, and a gear for directly directing the piston and input shaft together. The device provides a safe drive coupling that allows high torque transfer in direct dog drive.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a vacuum pump having a detachable drive coupling,

The present invention relates to a vacuum pump, and more particularly to a vacuum pump having a detachable drive coupling.

Generally, small and medium vehicles are equipped with a hydraulic brake system with vacuum assistance through a vacuum booster. Such systems are well known and need not be further described herein.

Historically, a vacuum source has been obtained from the inlet manifold of a gasoline engine or from a vacuum pump of a diesel engine. More recently, vacuum pumps have been provided for gasoline engine vehicles and diesel engine vehicles.

A dry, actuated vacuum pump driven by an electric motor has been proposed, but an oil lubricated mechanical driven vacuum pump is sometimes desirable for reliability and long life. Although other mechanical devices are possible, this pump is typically driven directly from the engine camshaft.

The engine driven pump rotates continuously and applies a small drag to the vehicle engine due to friction and pump losses. In particular, it is desirable to minimize such parasitic losses in order to improve the overall fuel consumption of the vehicle, for example because the vacuum pump may not be necessary for a long period of time when traveling on a highway with infrequent braking applications.

Provision of a detachable friction clutch is proposed in EP2049355A, whereby the drive to the pump rotor can be connected and disconnected as required. However, frictional drive under cold start conditions (-30 DEG C) may be problematic because a high drive torque may be required to remove the lubricating oil accumulated in the vacuum pump. This high torque may cause reduced clutch life, which is incompatible with safe operation. Further, the friction clutch can be physically wide.

Likewise, mechanical drive connections, such as dog clutches, are not considered practical due to shock loading when drive to the vacuum pump is connected.

What is required is a safe detachable drive for a vacuum pump. This allows cold starting engagement without impact loads, and preferably does not require electrical components or electrical connections.

According to a first aspect of the present invention there is provided a vacuum pump having a detachable drive coupling comprising an input shaft, a coaxial output shaft and an axially movable coupling sleeve of the shaft, Wherein the detachable drive coupling further comprises a speed synchronous clutch and a drive forming portion wherein the coupling sleeve is resiliently pushed into engagement with the input shaft engaged with the output shaft for rotation and wherein the input shaft rotates with the output shaft The coupling sleeve forms part of a movable annular piston in response to an increase in fluid pressure.

In use, a speed-synchromesh clutch is used to synchronize the input shaft and the output shaft before coupling the shafts together to exclude relative rotation. In the engaged state, the input shaft is directly coupled to the output shaft through a drive forming portion provided on both shafts. A fluid, preferably a liquid, under pressure is used to move the annular piston from the engaged position to the disengaged position. Preferably the liquid is a lubricating oil from an engine of a vehicle equipped with a vacuum pump.

In an embodiment, the input shaft is journalled within the output shaft, the output shaft defines a cylinder bore for the piston, and the piston is fixed against rotation against the cylinder bore.

In such an arrangement, the shafts may be disengaged, but may be coupled as required to continuously reduce the speed differential until the drive dog can be safely engaged. The speed synchronous clutch includes mutually engageable clutch surfaces associated with the driven and driven sides, one of which is movable against an elastic force.

The piston includes a base and a wall defining the sleeve, the dog drive being provided by a driven gear at the base engageable with the drive gear of the input shaft.

In an embodiment, the sleeve is circular and includes an inner clutch ring fixed in rotation with the sleeve and axially movable in the sleeve. The clutch ring defines a circular clutch surface engageable with a corresponding circular clutch surface of the input shaft. The clutch surface and the clutch ring together comprise a mechanism for synchronizing the rotational speed of the input shaft with the rotational speed of the piston.

The clutch surface may be defined by a single dry plate clutch, a wet multi-plate clutch or a cone clutch. Other types of clutches are also possible.

One of the clutch faces may be biased to the coupling by an elastic means acting between the input shaft and the clutch ring, and in the engaged state the piston may engage the shoulder of the input shaft. In one embodiment, the clearing ring is made of metal and is therefore substantially non-abrasive.

The driving portion of the present invention is elastically pushed by the engaging portion and thus is safe.

In an implementation, the drive includes a housing defining a bore defining a bearing for receiving an output shaft for rotation therein.

The output shaft preferably comprises a rotor of a vacuum pump, and the housing comprises a rotor chamber of a vacuum pump.

In an embodiment, the housing comprises an inlet for fluid under pressure, the inlet being open to the bearing and connected to the piston through the bearing to facilitate movement into the separated state; The inlet may be connected to the pump rotor via a bearing to facilitate lubrication of the pump rotor. Typically, lubricant for the engine is used for lubrication and operation of the drive coupling of the present invention when connected to the vehicle engine.

In another aspect, the invention includes a detachable drive of a vacuum pump, the detachable drive defining a rotational axis and defining a first cylindrical chamber about a rotational axis; An annular piston rotatably fixed to the first chamber and slidable in the first chamber along the axis of rotation; And a spring for urging the piston in one axial direction, the piston including a skirt defining a second cylindrical chamber about a base and an axis, the skirt being rotatably fixed with the piston and sliding along the axis of rotation in the second chamber, Wherein the input shaft and the clutch ring define a clutch surface that is mutually engageable, one clutch surface facing the base of the piston, the input shaft and the clutch ring facing the base of the piston and the input The shaft has mutually engageable gears for direct drive, whereby the axial movement of the piston in one direction to the shaft continues to engage the clutch surfaces and the other relative axial movement engages the gear.

In one embodiment, the input shaft and clutch ring define a tapered female and male clutch surface, the female clutch surface facing the piston to the base.

According to a further aspect of the present invention there is provided a detachable drive coupling comprising an input shaft, a coaxial output shaft and an axially movable coupling sleeve of the shaft, The coupling further includes a speed-synchronous clutch and a drive forming portion, wherein the coupling sleeve is resiliently pushed into engagement with the input shaft engaged with the output shaft for rotation, and wherein the input shaft is separated from the rotation with the output shaft To achieve the condition, the coupling sleeve forms part of a movable annular piston in response to an increase in fluid pressure.

In use, the speed-synchromesh clutch is used to synchronize the input shaft and the output shaft prior to coupling the shafts together to exclude relative rotation. In the engaged state, the input shaft is directly coupled to the output shaft through a drive forming portion provided on both shafts. A fluid, preferably a liquid, under pressure is used to move the annular piston from the engaged position to the disengaged position.

In an embodiment, the input shaft is journalled within the output shaft, the output shaft defines a cylinder bore for the piston, and the piston is fixed against rotation against the cylinder bore.

In such an arrangement, the shafts may be disengaged, but may be coupled as required to continuously reduce the speed differential until the drive dog can be safely engaged. The speed synchronous clutch includes mutually engageable clutch surfaces associated with the driven and driven sides, one of which is movable against an elastic force.

The piston includes a base and a wall defining the sleeve, the dog drive being provided by a driven gear at the base engageable with the drive gear of the input shaft.

In an embodiment, the sleeve is circular and includes an inner clutch ring fixed in rotation with the sleeve and axially movable in the sleeve. The clutch ring defines a circular clutch surface engageable with a corresponding circular clutch surface of the input shaft. The clutch surface and the clutch ring together comprise a mechanism for synchronizing the rotational speed of the input shaft with the rotational speed of the piston.

The clutch surface may be defined by a single dry plate clutch, a wet multi-plate clutch or a cone clutch. Other types of clutches are also possible.

One of the clutch faces may be biased by the resilient means acting between the input shaft and the clutch ring, and in the engaged state the piston may engage the shoulder of the input shaft. In one embodiment, the clutch ring is made of metal and is therefore substantially non-abrasive.

The driving portion of the present invention is resiliently pushed to the engaging portion and is thus secure.

In an embodiment, the drive includes a housing defining a bore defining a bearing to receive an output shaft for rotation therein.

The output shaft preferably comprises a rotor of a vacuum pump, and the housing comprises a rotor chamber of a vacuum pump.

In an embodiment, the housing comprises an inlet for fluid under pressure, the inlet being open to the bearing and connected to the piston through the bearing to facilitate movement into the separated state; The inlet may be connected to the pump rotor via a bearing to facilitate lubrication of the pump rotor. Typically, lubricant for the engine is used for lubrication and operation of the drive coupling of the present invention when connected to the vehicle engine.

Other features of the invention will be apparent from the following description of the preferred embodiments, which is given by way of example only in the accompanying drawings.

1 is a perspective view of one end of a vacuum pump included in the present invention;
Fig. 2 is a view corresponding to Fig. 1, showing a vacuum pump at another end; Fig.
Fig. 3 is an axial cross-sectional view through the pump of Figs. 1 and 2, and a vacuum pump is not shown.
Figs. 4 to 9 illustrate operation steps of the pump of Fig. 3; Fig.
Figures 10 to 12 illustrate a hydraulic element functional circuit.
Figure 13 shows a vacuum brake booster connected to a vacuum pump comprising the present invention.

Referring to Figure 1, a vacuum pump 10 according to the present invention includes a housing, which includes a rotor chamber 11, an expandable pump rotor 80, and a common type of sliding vane (not shown) Lt; / RTI > termination. If the pump mechanism is a rotating type, the type of pump mechanism is not related to the present invention. The end plate 12 closes the rotor chamber.

The pump rotor 80 is driven by an input shaft 13 in which the input shaft rotates within the small diameter end 15 of the pump body and is connected to a drive dock for engagement with one end of the camshaft of the internal combustion piston engine Drive dog 14, for example Oldham coupling. Other types of drive connections to the camshaft may be used. In practice, the entire small diameter end of the housing is inserted into the casing of the engine and therefore only a large diameter end can be seen in use. The separable drive coupling (20 in Figure 3) is in a vacuum pump, which is further described below.

As will be described, the pump rotor 80 includes an outer support surface 19 in the radial direction that advances into the bore 81 defined by the housing of the pump.

The pump chamber includes an inlet connection 16 that is adapted to be coupled to the vacuum hose of the brake booster and a check outlet valve 17.

In use, the pump rotates with the camshaft and pumps air from the inlet to the outlet to reduce the air pressure at the inlet side, thereby creating a partial vacuum in the brake booster vacuum chamber.

Figure 3 shows a cross-section through the small diameter end 15 of the pump of Figures 1 and 2; The pump chamber at the left side is omitted.

The pump housing 21 includes a cast of iron, aluminum or other suitable material, and defines the bearing of the output of the pump rotor or the support shaft 22 into which it can rotate. The shaft 22 and the pump rotor may be formed on a single integrated element.

The shaft 22 includes a closed circular chamber including a cylindrical bore 23, and the annular piston 24 reciprocates within the cylindrical bore along the axis of rotation. The piston 24 and the bore 23 are rotatably connected by a spline 25. The piston 24 is resiliently biased to the right end (as shown) of the bore 23 by the stack of oppositely disposed disc springs 26. Here, the disc spring is supported by the closed end of the bore 23. The piston includes a piston ring 27 for sealing against the wall of the bore 23. The input shaft 13, which is supported at both ends of the bore 23 by the plane bearing 29 and the support surface 29a, is rotatable within the piston 24. An oil seal (30) is also provided between the piston (24) and the shaft (13).

A clutch including a speed synchronizing mechanism is disposed between the input shaft 13 and the piston 24. The first circular clutch surface 31 is defined on the input shaft and is of a flat tapered shape toward the pump chamber. The second engagement clutch surface is defined by the circular clutch ring 32 in the piston 24. [ As will be explained, the ring 32 is rotationally fast with the piston 24 by the splines 33, but can move axially.

As shown, the ring 32 is resiliently biased to the right by a disc spring 34 that reacts to a cushion 35 engaged in the groove of the input shaft 13.

Disk springs 26 and 34 are conventional, but other types of elastic spring biases may be used if desired.

The clutch in this embodiment is a cone clutch, and any kind of plate clutch is also suitable. A wet multi-disc clutch is an alternative.

The piston includes a base 28 and a circumferential wall 28a defining a coupling sleeve. The piston base 28 further includes a drive forming portion including a driven gear 37 of a columnar arrangement. Here, the driven gear corresponds to the drive gear 36 in the circumferential arrangement around the input shaft 13. [ As shown in FIG. 3, the drive gear and the driven gear are engaged, but the relative axial movement of the piston to the left causes the gear to be separated. When engaged, the drive gear and driven gears 36 and 37, without circumferential action, provide direct drive from the input shaft 13 to the piston 26, as will be further described. The shoulder 38 of the input shaft limits the relative rightward movement of the piston 24.

The driving gear and the driven gears 36 and 37 include a drive dog of a detachable drive, but it is possible to reliably drive another type of movable shaft. A number of fine gears can provide easier engagement than fewer coarse gears. Depending on the materials available and the torque to be delivered, the skilled person can select the number and dimensions of the gears. Moreover, the precise shape of the gear is also selectable in view of the design considerations, taking into account the functional requirements of smooth engagement and disengagement and effective transmission of torque without substantial thrust in the axial direction.

For example, an appropriate connection allows the oil pressure from the engine-driven oil pump to pass through the wall of the pump housing 21 and through the groove 42 along the outer surface of the pump shaft 22 to the radial inlet 41 I go in. The pressurized oil then passes radially inwardly between the openings at the open end of the piston and is discharged axially through the drain passageway (43). The shuttle valve 44 is slidable in the bore 45 across the drain passageway and can move radially inward to seal the drain passageway if desired. As shown, the shuttle valve projects radially from the pump housing 21 in the open state.

The axial groove 46 in the interior of the pump housing allows the oil to pass to the left (shown in the figure) into the undercut 50 of the pump rotor, where the undercut can be part of the pump for lubrication purposes . Although circumferential grooves connecting the axial grooves 42 and 46 may be provided if necessary for the purpose of not exceeding the leakage of the oil to the pump rotor but being suitable for lubrication, It is contemplated that the film moves the oil from the groove 42 to the groove 46. A running clearance will be selected to give the proper volume flow of oil to the pump chamber sufficient to impart adequate lubrication and the flow rate can be determined empirically.

The oil under pressure can also leak to the left side of the piston (as viewed in the figure). This oil is allowed to escape through the radial and axial passageways 47 at the base of the bore 23 and through the central drain bore 48 of the input shaft 13 thereafter. During going to the bore 48, the oil may also lubricate the thrust washer 49. The escaping oil can also lubricate the coupling 14 before it is introduced back into the engine in any conventional manner.

3, the piston 24 is pushed to the right by the disc spring 26 and is moved to the piston at the input shaft and to the shaft 22 by the spline 25, The drive gear and the driven gears 36 and 37 are engaged with each other. Thus, the vacuum pump is driven at the speed of the input shaft, typically at the speed of the engine camshaft. In this state, oil under a pressure of typically 3 to 4 bar is fed to the inlet 41 and lubricates the drive device and the pump rotor of Fig. The drain passage 43 is wide enough to ensure that the oil pressure acting on the piston 24 is insufficient to overcome the elastic force of the disc spring 26. [

However, if the shuttle valve 44 is moved radially inward to seal the drain passage 43, the oil pressure will increase in the right portion of the piston 24 until the elastic force exerted by the disc spring is overcome . The piston 24 will eventually move to the left to disengage the drive and driven gears 36 and 37 and the clutch surface 31 from the ring 32. In this condition, the piston is no longer driven by the input shaft, and therefore the rotation of the pump rotor is stopped.

The entire operating sequence will be described with reference to Figs. 4-9.

Figure 4 shows a vacuum pump in an unactuated state; The shuttle valve 44 is closed and therefore the oil pressure is applied by pushing the piston 24 to the right to engage the drive and driven teeth 36 and 37 and the clutch ring 32 by the clutches 30 of the piston 24 . The piston 24, the shaft 22 and the pump rotor are stationary while the input shaft 13 is driven and rotated by the engine.

In Fig. 5, the shuttle valve 44 is opened, causing the pressure on the right side of the piston 24 to drop. As a result, under the elastic force of the disc spring 26, the piston starts to move to the right. The driving and driven gears 36 and 37 are not engaged but the clutch 30 releases the clutch ring 32 to bring the clutch ring into contact with the clutch surface 31 and consequently the clutch surface is in contact with the frictional force at the contact surface And starts to rotate. The piston 24 also begins to rotate by the spline 33 engaged with the clutch ring 32. [

In Figure 6, the piston moves further to the right, and after a short period of time the rotational speed of the piston 24 approaches the speed of the input shaft 13.

7, the rotational speed of the piston 24 and the rotational speed of the input shaft 13 are synchronized, and the rightward movement of the piston 24 is completed; The drive and driven gears 36 and 37 engage and the clutch interface including the speed synchronization mechanism does not transfer torque further from the input shaft 13 to the piston 24. [ The pump rotor 80 is directly driven by the input shaft.

8 shows the beginning of the separation, whereby the shuttle valve 44 is closed (radially inwardly moved) and therefore the pressure on the right side of the piston increases. As a result, the piston moves to the left, separating the drive gear and driven gears 36, 37 first, and then disconnecting the clutch 30 through the clutch 30, so that the components resume the non- do.

The shuttle valve 44 can be actuated in any suitable manner to couple the drive to the vacuum pump when needed. Although an electrical actuator can be used, a vacuum actuator is preferably provided that reacts directly to a vacuum consumer, e. G., A brake boost chamber. The separated vacuum thus causes the shuttle valve to move outward and couples the drive to the vacuum pump. The shuttle valve can be biased radially outwardly, for example, elastically biased to a coil compression spring to ensure safe operation, thereby coupling the drive in the absence of a vacuum signal (FIG. 7).

Any suitable material may be used for the vacuum pump of the present invention, and typically corresponds to the material used for the vacuum pump in the prior art.

The mounting of the pump to the vehicle engine may be in any suitable manner and may include a helical fastener through the hole 18 shown in FIG.

Although described in the context of a vacuum brake booster, a pump can of course be used to provide a vacuum for any other vacuum application of the vehicle. The protruding shuttle valve 44 provides a linear external actuation of the valve either axially or transversely through the sleeve or similar element and also provides a visual indication of engagement or disengagement.

The input shaft 13 and the clutch ring 32 are typically made of metal and have a substantially non-wear surface at the clutch interface and are lubricated by the oil from the input gallery 41.

The operation of the detachable drive coupling 20 is safe, and the resilient rightward force on the piston ensures drive engagement when there is not enough oil pressure to act on the piston. Also, due to the gradual speed matching of the input shaft and the output shaft, the dog drive provides that the high starting torque of the pump rotor can be overcome without an impact load.

Figure 10 is a CETOP functional hydraulic schematic of the device of the present invention showing the use of a shuttle valve 44 (not shown) for filling or emptying the chamber 62 of the piston 24 pushed to the left by the spring 26 Controls the oil source 60 under pressure. The shuttle valve is actuated by a vacuum in the control signal line 61 which indicates a vacuum demand. As indicated, the shuttle valve has two positions; The chamber 62 is connected to the drain 63 and to the clutch of the detachable drive coupling 20 when no vacuum signal is applied. Wherein the drive coupling includes a friction and dog clutch as previously described and connects the vehicle engine to a vacuum pump. As shown in Fig. 10, the coupling is engaged.

If the degree of vacuum of the control signal line 61 increases, the shuttle valve moves to an alternative state in which the outlet from the piston chamber 62 is blocked; The pressure in the piston chamber increases and the piston moves to the right (as shown) to separate the coupling. In this state, the vacuum pump is driven.

An alternative device is shown in Fig. 11, and common features in this device have the same reference numbers. In this case, the vacuum consumer includes a vacuum brake booster 72, and the engine 64 drives the vacuum pump 10 through the detachable drive coupling 20 of the present invention.

The vacuum reservoir 65 of the brake booster is connected to the vacuum pump 10 through a vacuum duct 66 where the vacuum duct includes a check valve 67.

The degree of vacuum in the reservoir 65 is indicated by the reference signal line 68 applied to the two-position vacuum valve 69. If the degree of vacuum is sufficient, then the vacuum valve 69 will adopt the state shown, where the control signal line 61 is connected to the atmosphere 70, and consequently the shuttle valve 44 will also have a chamber 62 The detachable drive coupling 20 is engaged by the inner spring 26 and is thus pierced in the control signal line 61. In this state, Or the vacuum valve 69 does not operate properly.

When the degree of vacuum in the reservoir 65 is sufficient, the vacuum valve 69 moves upward (as shown) from the position shown and connects the reservoir 65 to the control signal line 61. As a result, a vacuum is applied to the shuttle valve 44, which snaps to an alternative (elevated) condition in which the oil pressure from the engine acts on the piston 24 to disengage the drive coupling 20.

A lubricating passage 59 for the vacuum pump 10 is also shown in Fig.

Another alternative is shown in Fig. The apparatus of Fig. 12 is a simplified version of Fig. 11, wherein common components have the same reference numerals. The vacuum valve 69 of Fig. 11 is omitted, and the vacuum signal line 61 is directly connected to the reservoir 65. Fig. The operation of the embodiment of Figure 12 is the same as that for Figure 11 so that sufficient vacuum to separate the drive coupling 20 between the engine 64 and the vacuum pump 10 causes the shuttle valve to move up .

13 schematically illustrates an exemplary apparatus of the present invention for a vehicle hydraulic brake circuit, including a conventional brake master cylinder 71, a vacuum booster 72, a fluid reservoir 73 and a brake pedal 74; The hydraulic output of the master cylinder is indicated by arrow 75 and the vehicle structure is indicated by 76. [

Two vacuum connections from the vacuum chamber of the booster 72 to the vacuum pump 10, namely, a vacuum duct 66 for causing a vacuum pump to evacuate the brake booster when needed, and a control for indicating the degree of vacuum to the shuttle valve 44 A signal duct 61 providing a signal is provided. A check valve 67 may be provided in the vacuum duct 66 or in the brake booster vacuum connection. A drive shaft for the vacuum pump is shown at 77.

Modifications and improvements to the present invention are contemplated within the scope of the claims appended hereto.

10: Vacuum pump
11: Rotor chamber
12: End plate
13: input shaft
14: Driving dog (Oldham coupling)
15: Small diameter end
16: inlet connection
17: Check valve
18: Mounting hole
19: Support surface
20: Detachable drive coupling
21: Pump housing
22: Output shaft / pump rotor
23: cylinder bore
24: annular piston
25: spline
26: Disk spring
27: Piston ring
28: Piston base
28a: piston wall
29: Bearings
29a: Support surface
30: Oil seal
31: Clutch face of input shaft
32: clutch ring
33: Spline
34: Disk spring (Belleville washer)
35: Standing clip
36: Driving gear
37:
38: Shoulder
41: inlet
42: Groove
43: drain passage
44: Shuttle valve / exhaust valve
45: Shuttle valve bore
46: Axial groove
47: Radial and axial drain passage
48: center drain bore
49: Thrust washer
50: undercut
59: Lubrication path
60: Pressure oil source
61: control signal line
62: piston chamber
63: drain
64; Vehicle engine
65: Vacuum reservoir
66; Vacuum duct
67: Check valve
68; Reference signal line
69: Vacuum valve
70: waiting
71: Brake master cylinder
72: Vacuum booster
73: fluid reservoir
74: Brake pedal
75: Brake pressure
76: vehicle structure
77: drive shaft
80: Pump rotor
81: Rotor bore shaft

Claims (14)

The separable drive coupling 20 has an input shaft 13, a coaxial output shaft 22 and an axially movable coupling sleeve 20 of the shafts 13, Wherein the separable drive coupling 20 further comprises a speed synchronous clutch 31,32 and drive forming portions 36,37 which are arranged such that the input shaft 13 is connected to the output shaft 22 And in order to achieve a disengaged condition in which the input shaft 13 is separated from the rotation with the output shaft 22, the engagement sleeve is moved in response to an increase in the fluid pressure to a moveable annular piston 24 ). ≪ / RTI > 2. A method according to claim 1 wherein the input shaft is journalled within the output shaft and the output shaft defines a cylinder bore for the annular piston, (24) is fixed against rotation against the cylinder bore (23). 3. A device according to claim 1 or 2, wherein the annular piston (24) comprises a base (28) and a wall (28a) defining a sleeve (20) Is provided by a driven gear (37) at a base (28) engageable with a drive gear (36) of a motor. 4. An internal combustion engine according to claim 3, characterized in that the annular piston (24) comprises an internal clutch ring (32) fixed in rotation with the annular piston and axially movable of the annular piston, the clutch ring (32) ) Defining a tapered circular clutch surface (30) engageable with a corresponding circular clutch surface (31) of the clutch (10). 5. Vacuum pump (10) according to claim 4, characterized in that the clutch faces (30, 31) are biased to the coupling by means of elastic means (34) acting between the input shaft (13) and the clutch ring (32). 6. Vacuum pump (10) according to one of the claims 1 to 5, wherein the annular piston (24) engages with the shoulder (38) of the input shaft (13) in the engaged state. 7. Device according to one of claims 1 to 6, characterized in that the output shaft (22) has an axially extending, radially external support surface (19), and the drive part (20) A vacuum pump (10) further comprising a housing (21) defining a bore (81) for receiving a surface (19). A vacuum pump (10) as claimed in claim 7, characterized in that the output shaft (22) comprises a rotor (80) of a vacuum pump (10) and the housing ). 9. A device according to claim 8, comprising an inlet (41) for fluid under pressure in the housing (21), the inlet (16) being open to the support surface (19) and passing through the support surface (19) ) To facilitate movement into a disengaged state. 10. Vacuum pump (10) according to claim 9, wherein the inlet (41) is connected to the pump rotor (80) via a support surface (19) to facilitate lubrication of the inlet. 11. Vacuum pump (10) according to claim 9 or 10, further comprising an exhaust valve (44) in the housing (21), thereby relieving the fluid pressure acting on the annular piston (24) if necessary. The vacuum pump according to claim 11, wherein the exhaust valve (44) further comprises a spool valve (44) slidable in the bore (45) from the open state to the closed state to shut off the fluid drain passage (43) 10). The vacuum pump (10) according to claim 12, wherein the spool valve (44) is protruded from the housing (21) in an open state. A vehicle engine (64) comprising the vacuum pump (10) of any one of claims 1 to 13.

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